The present invention relates to ink jet printing and more particularly to a fluid supply cartridge for an ink jet printer such as a continuous ink jet printer.
In ink jet printing systems the print is made up of individual droplets of ink generated at a nozzle and propelled towards a substrate. There are two principal systems: drop on demand where ink droplets for printing are generated as and when required; and continuous ink jet printing in which droplets are continuously produced and only selected ones are directed towards the substrate, the others being recirculated to an ink supply.
Continuous ink jet printers supply pressurized ink to a print head drop generator where a continuous stream of ink emanating from a nozzle is broken up into individual regular drops by, for example, an oscillating piezoelectric element. The drops are directed past a charge electrode where they are selectively and separately given a predetermined charge before passing through a transverse electric field provided across a pair of deflection plates. Each charged drop is deflected by the field by an amount that is dependent on its charge magnitude before impinging on the substrate whereas the uncharged drops proceed without deflection and are collected at a gutter from where they are recirculated to the ink supply for reuse. The charged drops bypass the gutter and hit the substrate at a position determined by the charge on the drop and the position of the substrate relative to the print head. Typically the substrate is moved relative to the print head in one direction and the drops are deflected in a direction generally perpendicular thereto, although the deflection plates may be oriented at an inclination to the perpendicular to compensate for the speed of the substrate (the movement of the substrate relative to the print head between drops arriving means that a line of drops would otherwise not quite extend perpendicularly to the direction of movement of the substrate).
In continuous ink jet printing a character is printed from a matrix comprising a regular array of potential drop positions. Each matrix comprises a plurality of columns (strokes), each being defined by a line comprising a plurality of potential drop positions (e.g. seven) determined by the charge applied to the drops. Thus each usable drop is charged according to its intended position in the stroke. If a particular drop is not to be used then the drop is not charged and it is captured at the gutter for recirculation. This cycle repeats for all strokes in a matrix and then starts again for the next character matrix.
Ink is delivered under pressure to the print head by an ink supply system that is generally housed within a sealed compartment of a cabinet that includes a separate compartment for control circuitry and a user interface panel. The system includes a main pump that draws the ink from a reservoir or tank via a filter and delivers it under pressure to the print head. As ink is consumed the reservoir is refilled as necessary from a replaceable ink cartridge that is releasably connected to the reservoir by a supply conduit. The ink is fed from the reservoir via a flexible delivery conduit to the print head. The unused ink drops captured by the gutter are recirculated to the reservoir via a return conduit by a pump. The flow of ink in each of the conduits is generally controlled by solenoid valves and/or other like components.
As the ink circulates through the system, there is a tendency for it to thicken as a result of solvent evaporation, particularly in relation to the recirculated ink that has been exposed to air in its passage between the nozzle and the gutter. To compensate for this, “make-up” solvent is added to the ink as required from a replaceable ink cartridge so as to maintain the ink viscosity within desired limits. This solvent may also be used for flushing components of the print head, such as the nozzle and the gutter, in a cleaning cycle.
The ink and solvent cartridges are filled with a predetermined quantity of fluid and generally releasably connected to the reservoir of the ink supply system by a flexible supply hose or tube so that the reservoir can be intermittently topped-up by drawing ink and/or solvent from the cartridges as required. To ensure the cartridges are brought into correct registration with the supply hoses they are typically connected to the ink supply system via a docking station comprising a cartridge holder. When the cartridges are correctly docked fluid communication with an outlet port of the cartridge is ensured.
It is important from the manufacturer's perspective that the ink jet printer is consumes only ink (or solvent) of the correct type and quality. If a cartridge containing the wrong ink is used the printing quality can be compromised and, in extreme cases, printer failure may be caused. It has thus become the convention to provide the cartridge with an externally machine readable label (e.g. a bar code) carrying information regarding the fluid contained within the cartridge. The label is swiped past a reader associated with the control system of the printer before the cartridge is installed and only when the control system of the printer has read the information on the label and verified that the ink is suitable for operation with the printer does it allow ink or solvent to be drawn from the cartridge.